9 charts that reveal how the American middle class has declined since 1970

"After more than four decades of serving as the nation's economic majority, the American middle class is now matched in number by those in the economic tiers above and below it," writes the Pew Research Center in a report that analyzes the changing size, demographic, and economic status of the American middle class.

Pew Research defines middle class as "those with an income that is 67% to 200% (two-thirds to double) of the overall median household income, after incomes have been adjusted for household size. Lower-income households have incomes less than 67% of the median, and upper-income households have incomes that are more than double the median."

In addition to no longer being the majority, income growth for this segment of Americans is sluggish, the report finds. Since 1970, median income has risen for all classes of households, but the increase for upper-income households has outpaced the middle class increase by 13 percentage points. (And middle class median income outpaced that among lower-income households by another six percentage points.)

"The state of the American middle class is at the heart of the economic platforms of many presidential candidates ahead of the 2016 election," Pew Research writes. "Policymakers are engaged in debates about the need to raise the floor on wages and on how best to curb rising income inequality."

Read on to see the changing face of the middle class in nine revealing charts:

For context, here's the household income required to be considered middle class and upper class, adjusted for household size:

In 1971, the middle class represented the majority of American earners. In 2015, 120.8 million adults were in middle-income households, less than the 121.3 million who were in lower- and upper-income households combined.

As the upper class has grown in size, America's aggregate income has shifted away from the middle class. In 1970, the middle class held 62% of America's aggregate household income and the upper class held 29% — in 2014, the middle class held 43%, while the upper class held 49%.

The percentage of middle class Americans has fallen from 61% in 1971 to 50% in 2015. Meanwhile, the percentage living in the upper-income tier rose from 14% to 21% over the same period.

Here's a similar chart allowing you to see how the middle class is being squeezed over time by the increasing percentage of those in the lower and upper class:

The middle class is falling further behind financially. You can see that the income of middle-class Americans hasn't grown nearly as much as the income of those in the upper class since 1970.

Here's another way of visualizing it. The upper class median household income has increased by $56,008 since 1970, while the middle class median household income has increased by $18,710 in the same period.

Household income rose for all classes in each decade from 1970 to 2000, but declined from 2000 to 2010, thanks to the 2001 recession and the Great Recession of 2007 to 2009. Only the upper-income families have started to recover.

Upper-income families, which had three times as much wealth as middle-income families in 1983, had seven times as much in 2013. The wealth gap is only widening.